Consuming a RESTful Web Service

如果不知道如何使用 Spring，请先查看 Building a RESTful Web Service。

官方文章地址：https://spring.io/guides/gs/consuming-rest/

下载地址

git clone https://github.com/spring-guides/gs-consuming-rest.git

实现示例：使用 RestTemplate 访问 Spring 的 RESTful 接口， 随机获取 Spring 的一段文字 http://gturnquist-quoters.cfapps.io/api/random 。

build.gradle 文件：

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:1.5.2.RELEASE")
    }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'idea'
apply plugin: 'org.springframework.boot'

jar {
    baseName = 'gs-consuming-rest'
    version =  '0.1.0'
}

repositories {
    mavenCentral()
}

sourceCompatibility = 1.8
targetCompatibility = 1.8

dependencies {
    compile("org.springframework.boot:spring-boot-starter")
    compile("org.springframework:spring-web")
    compile("com.fasterxml.jackson.core:jackson-databind")
    testCompile("junit:junit")
}

我们要获取的数据例子如下：

{
   type: "success",
   value: {
      id: 10,
      quote: "Really loving Spring Boot, makes stand alone Spring apps easy."
   }
}

先创建一个 src/main/java/hello/Quote.java 实体类来接收数据：

package hello;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

@JsonIgnoreProperties(ignoreUnknown = true)
public class Quote {

    private String type;
    private Value value;

    public Quote() {
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public Value getValue() {
        return value;
    }

    public void setValue(Value value) {
        this.value = value;
    }

    @Override
    public String toString() {
        return "Quote{" +
                "type='" + type + '\'' +
                ", value=" + value +
                '}';
    }
}

下面来创建 src/main/java/hello/Value.java 类：

package hello;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

@JsonIgnoreProperties(ignoreUnknown = true)
public class Value {

    private Long id;
    private String quote;

    public Value() {
    }

    public Long getId() {
        return this.id;
    }

    public String getQuote() {
        return this.quote;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public void setQuote(String quote) {
        this.quote = quote;
    }

    @Override
    public String toString() {
        return "Value{" +
                "id=" + id +
                ", quote='" + quote + '\'' +
                '}';
    }
}

在 Application 中使用 RestTemplate 获取数据：

public class Application {

    private static final Logger log = LoggerFactory.getLogger(Application.class);

    public static void main(String args[]) {
        RestTemplate restTemplate = new RestTemplate();
        Quote quote = restTemplate.getForObject("http://gturnquist-quoters.cfapps.io/api/random", Quote.class);
        log.info(quote.toString());
    }

}

RestTemplate 使用 message converter 将返回的 json 字符串转换为 Quote 类。
RestTemplate 可发送 GET、POST、PUT、DELETE 请求，这里使用的是 GET 请求。

上面的 Application 中我们还没有使用到 Spring Boot，下面来看看如何使用：

package hello;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
public class Application {

    private static final Logger log = LoggerFactory.getLogger(Application.class);

    public static void main(String args[]) {
        SpringApplication.run(Application.class);
    }

    @Bean
    public RestTemplate restTemplate(RestTemplateBuilder builder) {
        return builder.build();
    }

    @Bean
    public CommandLineRunner run(RestTemplate restTemplate) throws Exception {
        return args -> {
            Quote quote = restTemplate.getForObject(
                    "http://gturnquist-quoters.cfapps.io/api/random", Quote.class);
            log.info(quote.toString());
        };
    }
}

Spring 会自动诸如 RestTemplateBuilder ，然后会将 RestTemplate 注入 @Bean 中。

执行会输出如下日志：

2017-06-11 12:30:47.691  INFO 4805 --- [           main] hello.Application                        : Quote{type='success', value=Value{id=6, quote='It embraces convention over configuration, providing an experience on par with frameworks that excel at early stage development, such as Ruby on Rails.'}}